Counterbore Pocket Structure for Fluidic Assembly

ABSTRACT

A fluidic assembly method is provided that uses a counterbore pocket structure. The method is based upon the use of a substrate with a plurality of counterbore pocket structures formed in the top surface, with each counterbore pocket structure having a through-hole to the substrate bottom surface. The method flows an ink with a plurality of objects over the substrate top surface. As noted above, the objects may be micro-objects in the shape of a disk. For example, the substrate may be a transparent substrate and the disks may be light emitting diode (LED) disks. Simultaneously, a suction pressure is created at the substrate bottom surface. In response to the suction pressure from the through-holes, the objects are drawn into the counterbore pocket structures. Also provided is a related fluidic substrate assembly.

RELATED APPLICATIONS

This application is a Continuation-in-part of an application entitled,LIGHT EMITTING DIODE (LED) USING THREE-DIMENSIONAL GALLIUM NITRIDE (GaN)PILLAR STRUCTURES, invented by M. Albert Crowder et al., Ser. No.14/088,374, filed Nov. 23, 2013, attorney docket no. SLA3086.2;

which is a Continuation of an application entitled, LIGHT EMITTING DIODE(LED) USING THREE-DIMENSIONAL GALLIUM NITRIDE (CaN) PILLAR STRUCTURESWITH PLANAR SURFACES, invented by M. Albert Crowder et al., Ser. No.13/367,120, filed Feb. 6, 2012, attorney docket no. SLA3086.1;

which is a Continuation-in-Part of an application entitled, METHOD FORFABRICATING THREE-DIMENSIONAL GALLIUM NITRIDE STRUCTURES WITH PLANARSURFACES, invented by M. Albert Crowder et al., Ser. No. 13/337,843,filed Dec. 27, 2011, attorney docket no. SLA3086. All these applicationsare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention, generally relates to integrated circuit (IC) fabricationand, more particularly, to a fluidic assembly process for the placementof microstructures on an IC substrate.

2. Description of the Related Art

The transfer of microfabricated electronic devices, optoelectronicdevices, and sub-systems from a donor substrate/wafer to a large areaand/or unconventional substrate provides a new opportunity to extend theapplication range of electronic and optoelectronic devices. For example,display pixel size light emitting diode (LED) micro structures, such asrods, fins or disks, can be first fabricated on small size wafers andthen be transferred to large panel glass substrate to make a directemitting display.

Existing transfer techniques such as inkjet printing, roboticpick-and-place, and fluidic self-assembly work reasonable well incertain particular applications. However, these conventional techniquesare either not cost effective or so poor in yield that they cannot beapplied to directly transfer LED micro structures.

It would be advantageous if microstructure objects could be preciselylocated on a substrate using a low cost method with a high yield.

SUMMARY OF THE INVENTION

Disclosed herein is a counterbore pocket structure for micro-objectfluidic assembly, where the micro-objects may, for example, be lightemitting diode (LED) micro disks. A “keyhole” shape pocket combines theadvantages of a second circular pocket with a loose tolerance, for easydisk capture, and a first circular pocket with a tighter tolerancehaving a zero or minimum disk-to-pocket gap. In addition, thearrangement of a through-hole, off center from the narrow part of thepocket, enhances the suction force on the captured micro disk, so thatthe disk is pulled towards the appropriate position until it forms atight contact with the edge of the pocket, achieving the desirablenear-zero gap between the pocket and the disk.

Moreover, a modification on the wide part of the keyhole shapecounterbore pocket prevents an “extra” micro disk from becoming trappedin the wide part of the pocket. By modifying the wide part of thekeyhole shape pocket from a simple circular shape to a “third-quartercrescent moon” shape, the crescent moon pocket shape only captures asingle micro disk, while inheriting all the advantages on the circulardesign.

The counterbore pocket structure not only improves efficiency and yieldin a fluidic based LED micro structures distribution process, but alsorelaxes the requirements on subsequent fabrication steps. For example,the near-zero gap between the pocket edge and the disk makes thepassivation and planarization processes much easier so that, again, bothfabrication yield and long term reliability are improved significantly.

Accordingly, a fluidic assembly method is provided that uses acounterbore pocket structure. The method is based upon the use of asubstrate with a plurality of counterbore pocket structures formed inthe top surface, with each counterbore pocket structure having athrough-hole, to the substrate bottom surface. The method flows an inkwith a plurality of objects over the substrate top surface. As notedabove, the objects may be micro-objects in the shape of a disk. Forexample, the substrate may be a transparent substrate and the disks maybe LED disks. Simultaneously, a suction pressure is created at thesubstrate bottom surface. In response to the suction pressure from thethrough-holes, the objects are drawn into the counterbore pocketstructures.

In one aspect, the counterbore pocket structures have a sliding fitdiameter to accommodate a disk diameter that permits a disk to rotate orslide freely in the pocket. Alternatively, the counterbore pocketstructures have a keyhole shape with a first portion overlying thethrough-hole having a first diameter sliding or transition fit toaccommodate a disk diameter, and a second portion overlapping the firstportion, having a second diameter greater than the first diameter. Inone variation, the through-hole is offset from the first diametercenter, away from the second portion. In another variation, the secondportion has a crescent moon-shape with a second diameter greater thanthe first diameter.

More explicitly, the step of flowing the ink over the substrate topsurface may involve arranging the substrate top surface with a substratefirst side higher than a substrate second side, and introducing the inkto the substrate first side. Then, the disks are drawn into thecounterbore pocket structures in response to gravity as well as suctionpressure.

Additional details of the above-described method, as well a fluidicsubstrate assembly, are provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a fluidic assemblysubstrate.

FIG. 2 is a plan view depicting a first variation of the fluidicassembly substrate in detail.

FIG. 3 is a plan view depicting a second variation of the fluidicassembly structure in detail.

FIG. 4 is a plan view depicting a third variation of the fluidicassembly structure in detail.

FIGS. 5A through 5D are perspective views depicting a fluidic assemblyprocess.

FIGS. 6A through 6F are perspective views depicting problems that mayoccur as a result of tolerance issues.

FIG. 7 is a perspective view depicting an exemplary keyhole shapecounterbore pocket structure.

FIGS. 8A through 8D are perspective views depicting a fluidic assemblyprocess using the keyhole shape counterbore pocket structure.

FIG. 9 depicts a potential issue that may affect the keyhole shapecounterbore pocket structure of FIG. 3 and FIGS. 8A-8D.

FIGS. 10A through 10C depict process steps associated with the keyholecounterbore pocket structure of FIG. 4.

FIG. 11 is a flowchart illustrating a fluidic assembly method using acounterbore pocket structure.

FIG. 12 is a partial cross-sectional view depicting a variation of thefluidic assembly substrate of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 is a partial cross-sectional view of a fluidic assemblysubstrate. The fluidic assembly substrate 100 comprises a substrate 102with a top surface 104 and a bottom surface 106. In one aspect, thesubstrate 102 may be transparent to visible spectrum light, such asmight be useful in the fabrication of electronic displays and opticalsensors. A plurality of counterbore pocket structures are formed in thesubstrate top surface 104, designated as 108-0 through 108-n, where n isnot limited to any particular positive integer value. Through-holes,110-0 through 110-n are respectively formed between each counterborepocket structure 108-0 through 108-n and the substrate bottom surface106. As used herein, a the word “counterbore” is understood to be arecess, which is typically cylindrical, around a hole in a surfaceplane. It is also typical that object inserted into the counterbore isintended to be flush (level) with the surface plane. Although examplesof circular and keyhole shaped pocket structures are provided below, itshould be understood that the pocket structure is not necessarilylimited to any particular shape. In one aspect, a finished substrateassembly would further comprise objects 112-0 through 112-n at leastsliding fit-positioned inside each counterbore pocket structure 108-0through 108-n, respectively. Alternatively, the objects may be atransition fit inside the counterbore pocket structure. Again, althoughdisk structures are mentioned below as an example, the assembly is notnecessarily limited to any particular object shape. In one aspect, theobject 112 is a light emitting diode (LED) disk. In another aspect, theobjects are photodiodes (PDs), which may also be formed in the shape ofa disk.

As used herein, the word “fit” refers to the mating of two mechanicalcomponents. Manufactured parts are very frequently required to mate withone another. They may be designed to slide freely against one another orthey may be designed to bind together to form a single unit or assembly.There are three general categories of fits. A clearance fit may bedesirable for an object to rotate or slide freely within thecounterbore, this is usually referred to as a “sliding fit.” Aninterference fits may be desirable for when as object is to be securelyheld within the counterbore, this is usually referred to as aninterference fit. A transition fits may be desirable for when the objectis to be held securely, yet not so securely that it cannot bedisassembled or rotated in the counterbore, this is usually referred toherein as a location or transition fit.

FIG. 2 is a plan view depicting a first variation of the fluidicassembly substrate in detail. In this aspect, counterbore pocketstructure 200 has a first diameter 202. In a substrate assembly, thecounterbore, pocket structure first diameter 202 forms a sliding toaccommodate a disk 204 with a diameter 206. Alternatively, the fit maybe a transition fit. Typically, the second diameter is larger than aclearance (sliding) fit so that it can enable easy capture of a microdisk, while being no larger than approximate 1.5× of the disk'sdiameter, so that the counterbore pocket structure does not trap morethan one disk.

FIG. 3 is a plan view depicting a second variation of the fluidicassembly structure in detail. In this aspect, counterbore pocketstructure 300 has a keyhole shape with a first portion 302 overlying athrough-hole 304, having a first diameter 306. A second portion 308overlaps the first portion (as shown in phantom) and has a seconddiameter 310 greater than the first diameter. In another variation, thethrough-hole 304 is offset from the first diameter center 312, away fromthe second portion 308, as shown in phantom. In a substrate assembly,the first diameter 306 may be either a sliding fit or a transition fitto accommodate a disk 314 with a disk diameter 316.

FIG. 4 is a plan view depicting a third variation of the fluidicassembly structure in detail. In this aspect, the counterbore pocketstructure 400 has a keyhole shape with a first portion 402 overlying thethrough-hole 404, with a first diameter 406. A second portion 408overlaps the first portion 402, and has a crescent moon-shape, orthree-quarters crescent moon-shape, with a second diameter 410 greaterthan the first diameter 406. In a substrate assembly, the first diameter406 may be either a sliding fit or a transition fit to accommodate adisk 412 with a disk diameter 414. As in FIG. 3, the through-hole 404may be offset away from the second portion 408, as shown in phantom.

A fluidic assembly technique permits the distribution of fabricatedobjects, such as LED micro structures in the form of disks, to beexactly placed on a substrate. Exact placement permits subsequentinterconnection processes, even though the disks are very small in size.Initially, an ink is prepared as follows. The LED micro disks are firstfabricated on a small substrate. The LED micro disks are harvested usinglaser liftoff, when the disks are gallium nitride (GaN) for example, orwet chemical etch, when the disks are gallium indium arsenide phosphide(GaInAsP) for example, and form an ink in a solvent. The targetsubstrate is prepared as follows. An array of through-holes isfabricated in a large area substrate such as glass. Counterbore holesare formed with a diameter slighter larger than LED micro disk diameter,to a depth equal to the LED micro disk thickness, overlying thethrough-holes, either by direct etch into the same substrate or on alaminated second layer thin film which has the same thickness as themicro disks (see FIG. 12).

FIGS. 5A through 5D are perspective views depicting a fluidic assemblyprocess. A through-hole 502 is formed in the substrate 500, as shown inFIG. 5A. In FIG. 5B, the counterbore 504 is formed over the through-hole502. The substrate is then mounted into the fluidic assembly system atan optimal tilting angle. In FIG. 5C the carrier fluid (ink) flows overthe top surface due to the gravity and a suction pressure from thesubstrate bottom by vacuum via the through-hole 502. In FIG. 5D, an LEDmicro disk 506 falls into the counterbore pocket structure, and caps thethrough-hole 502.

FIGS. 6A through 6F are perspective views depicting problems that mayoccur as a result of tolerance issues. One challenge is the selection ofthe tolerance between the counterbore pocket diameter and the micro diskdiameter. If the tolerance is too tight, then there is a chance thatstiction may cause a micro disk 506 to “hang” on the edge of thecounterbore pocket structure, as shown in FIG. 6A. However, while alarge tolerance may avoid the sticking pocket edge issue of FIG. 6A, therandom distributions of the disk 506 inside the counterbore, pocketstructure, as shown in FIGS. 6B through 6F, make the post distributionprocesses very difficult due to the random distributed gap between themicro disk and the counterbore pocket structure.

FIG. 7 is a perspective view depicting an exemplary keyhole shapecounterbore pocket structure. The keyhole structure addresses both theproblem of randomly distributed disks, by aligning the disks inpredictable positions, and the problem of stiction due to too tight atolerance. Instead of using a highly symmetric circular shapecounterbore pocket structure, a keyhole shape counterbore pocketstructure 701 has a wide part (second portion) 702 formed in substrate700, with a larger diameter to more easily capture a micro disk, as wellas a narrow part (first portion) 704 with a tighter tolerance to lockthe trapped micro disk into a predetermined position. In addition, thethrough-hole 706 is arranged off the center of the narrow part 704 ofpocket so that a micro disk becomes positioned at the top of thethrough-hole, with a minimum gap between the pocket edge and the microdisk.

FIGS. 8A through 8D depicting a fluidic assembly process using thekeyhole shape counterbore, pocket structure. In FIG. 8A the substrate700 with the keyhole shape counterbore, pocket structure 701 is thenmounted into the fluidic assembly system at an optimal tilting angle,and the carrier fluid flows over the top surface due to the gravity anda pulling pressure on the bottom by vacuum via the through-holes. Asuspended micro disk 800 may be pushed and pulled by the flow from rightto left. Once approaching the counterbore pocket structure 701, themicro disk 800 falls inside the counterbore pocket structure 701 withoutdifficulty since the wide part of the counterbore pocket structure 701has larger diameter than the micro disk, as shown in FIGS. 8B and 8C. InFIG. 8D, the micro disk 800 inside the counterbore pocket structure 701continues moving towards the narrow part 704 of the counterbore pocketstructure 701 due to the suction pressure via the through-hole 706.Since the through-hole 706 is arranged off the center of the narrow part704 of the packet, the suction pressure keeps pulling the micro disk 800until the micro disk's edge 802 (left on the drawing page) contacts thepocket edge 804 (left on the drawing page), forming a tight fit andcapping the through-hole. Thus, the micro disk 800 has been placed in apredetermined position on the substrate with a near zero gap to thecounterbore pocket structure 701 edge.

Distributing the micro disk into predetermined positions on thesubstrate significantly improves the fabrication yield in subsequentprocess steps, as the near zero gap between the micro disk and thecounterbore pocket structure edge makes interconnections on arrayedmicro disks array practical. For example, a simple passivation can alsoserve as planarization to reduce the step height in the gap so thatstandard interconnections process can be adopted without significantmodifications, which also improves the interconnection yield.

FIG. 9 depicts a potential issue that may affect the keyhole shapecounterbore pocket structure of FIG. 3 and FIGS. 8A-8D. After one microdisk 800 has been inserted into the lock position, another micro disk900 could also be trapped into the wide part 702 of the counterborepocket structure, as illustrated. This at least is a waste of microdisks.

FIGS. 10A through 10C depict process steps associated with the keyholecounterbore pocket structure of FIG. 4. This crescent moon keyholestructure addresses the above-presented problem presented in thedescription of FIG. 9. As shown in FIG. 10A, a “third-quarter crescentmoon” shape is used to replace the circular shape in the wide part 1002of the keyhole shape counterbore pocket structure 1000. FIGS. 10B and10C illustrate the micro disk distribution procedure using the modifiedcounterbore pocket structure 1000. As shown, after one micro disk 1004has been inserted into the lock position, there is no room for anothermicro disk to be accommodated.

In summary, the keyhole shape counterbore pocket structure is composedof a narrow circular part which has a tight tolerance with respect tothe micro disk and a wide circular part which has looser tolerance withrespect to the micro disk. The two parts are merged together along theircommon tangent lines. The counterbore pocket structure depth is equal to(or close to) the micro disk thickness, and is either etched into aglass substrate or formed on a laminated thin layer film. Thecounterbore pocket structure is able to enhance the performance of afluidic based LED micro disk distribution process in at least threeaspects:

1) The structure captures a micro disk in the flow easily, since thediameter of the wide part of the pocket is larger than the micro disk.

2) The arrangement of the through-hole, off center from the narrow partof the pocket, enhances the suction force on the captured micro disk sothat the disk pulls into the predetermined position, forming a tightcontact with the edge of the counterbore pocket structure.

3) The tight tolerance of the micro disk in the narrow part of thepocket makes passivation and planarization much easier, so that bothfabrication yield and long term reliability are improved significantly.

Further, to overcome a potential issue of capturing an extra disk in thewide part of the counterbore pocket structure, a modification replacesthe circular wide part with a “third-quarter crescent moon” shape, sothat the new pocket shape only captures one micro disk, while inheritingall the advantages of the original design.

FIG. 11 is a flowchart illustrating a fluidic assembly method usingcounterbore, pocket structure. Although the method is depicted as asequence of numbered steps for clarity, the numbering does notnecessarily dictate the order of the steps. It should be understood thatsome of these steps may be skipped, performed in parallel, or performedwithout the requirement of maintaining a strict order of sequence.Generally however, the method is associated with the above-describedfigures and follows the numeric order of the depicted steps. The methodstarts at Step 1100.

Step 1102 provides a substrate comprising a top surface and a bottomsurface, with a plurality of counterbore pocket structures formed in thetop surface. Each counterbore pocket structure has a through-hole to thesubstrate bottom surface. Step 1104 flows an ink comprising a pluralityof objects over the substrate top surface. In one aspect, the objectsare in the shape of a disk. If so, Step 1102 provides counterbore pocketstructures having a first diameter sliding fit to accommodate a diskdiameter. Alternatively, the first diameter may be a transition fit. Inanother aspect, the substrate is transparent, and Step 1104 flows an inkcomprising a plurality of LEDs or PDs in the shape of a disk over thesubstrate top surface. Step 1106 creates a suction pressure at thesubstrate bottom surface. In response to the suction pressure from thethrough-holes, Step 1108 draws the objects into the counterbore pocketstructures.

In one variation, Step 1102 provides counterbore pocket structureshaving a keyhole shape with a first portion overlying the through-hole,with a first diameter transition fit to accommodate a disk diameter.Alternatively, the first diameter may form a sliding fit. Thecounterbore pocket structure has a second portion overlapping the firstportion, with a second diameter greater than the first diameter. In oneaspect, Step 1102 provides the through-hole offset from the firstdiameter center, away from the second portion.

In another variation, Step 1102 provides counterbore pocket structureshaving a keyhole shape with a first portion overlying the through-hole,with a first diameter transition (or sliding) fit to accommodate a diskdiameter, and a second portion overlapping the first portion, having acrescent moon-shape with a second diameter greater than the firstdiameter. In one aspect, Step 1102 provides the through-hole offset fromthe first diameter center, away from the second portion.

In one aspect, flowing the ink over the substrate top surface in Step1104 includes the following substeps. Step 1104 a arranges the substratetop surface with a substrate first side higher than a substrate secondside. Step 1104 b introduces the ink to the substrate first side. Then,Step 1108 draws the disks in response to gravity, as well as suctionpressure.

FIG. 12 is a partial cross-sectional view depicting a variation of thefluidic assembly substrate of FIG. 1. In this aspect, the fluidicassembly substrate 100 comprises a first layer 1200, with through-holes1202 formed between the top surface 1204 and bottom surface 1206. Forexample, the first layer 1200 may be glass. A thin-film 1208 is formedis formed over the first layer 1200 with counterbore pocket structures1210 between a top surface 1212 and a bottom surface 1214, over thethrough-holes 1202. The counterbore pocket structures 1210 may becircular in shape, as shown in FIG. 2, or have the keyhole shapes ofFIG. 3 or 4 (not shown in this figure). In one aspect, the thin-film1208 is transparent. When assembled, the substrate assembly furthercomprises objects 1216 occupying the counterbore pocket structures 1210.

A substrate assembly and associated fluidic assembly process have beenprovided. Examples of shapes, materials, and uses have been presented toillustrate the invention. However, the invention is not limited tomerely these examples. Other variations and embodiments of the inventionwill occur to those skilled in the art.

We claim:
 1. A fluidic assembly method using a counterbore pocketstructure, the method comprising: providing a substrate comprising a topsurface and a bottom surface, with a plurality of counterbore pocketstructures formed in the top surface, with each counterbore pocketstructure having a through-hole to the substrate bottom surface; flowingan ink comprising a plurality of objects over the substrate top surface;creating a suction pressure at the substrate bottom surface; and, inresponse to the suction pressure from the through-holes, drawing theobjects into the counterbore pocket structures.
 2. The method of claim 1wherein flowing the ink over the substrate top surface includes flowingan ink comprising a plurality of objects in a shape of a disk.
 3. Themethod of claim 2 wherein providing the substrate includes providingcounterbore pocket structures having a first diameter sliding fit toaccommodate a disk diameter.
 4. The method of claim 2 wherein providingthe substrate includes providing counterbore pocket structures having akeyhole shape with a first portion overlying the through-hole, with afirst diameter transition fit to accommodate a disk diameter, and asecond portion overlapping the first portion, having a second diametergreater than the first diameter.
 5. The method of claim 4 whereinproviding the substrate includes providing the through-hole offset fromthe first diameter center, away from the second portion.
 6. The methodof claim 2 wherein providing the substrate includes providingcounterbore pocket structures having a keyhole shape with a firstportion overlying the through-hole, with a first diameter transition fitto accommodate a disk diameter, and a second portion overlapping thefirst portion, having a crescent moon-shape with a second diametergreater than the first diameter.
 7. The method of claim 1 whereinflowing the ink over the substrate top surface includes: arranging thesubstrate top surface with a substrate first side higher than asubstrate second side; introducing the ink to the substrate first side;and, wherein drawing disks into the counterbore pocket structuresincludes drawings the disks in response to gravity as well as suctionpressure.
 8. The method of claim 1 wherein providing the substrateincludes providing a transparent substrate; and, wherein flowing the inkover the substrate top surface includes flowing a plurality of lightemitting diodes (LEDs) in the shape of a disk over the substrate topsurface.
 9. A fluidic assembly substrate comprising: a substratecomprising a top surface and a bottom surface; a plurality ofcounterbore pocket structures formed in the substrate top surface; and,a through-hole formed between each counterbore pocket structure and thesubstrate bottom surface.
 10. The fluidic assembly substrate of claim 9wherein the substrate comprises: a first layer with through-hole,sformed between a first layer top surface and a first layer bottomsurface; and, a second layer with counterbore pocket structure formedbetween a second layer top surface and a second layer bottom surface.11. The fluidic assembly substrate of claim 9 wherein the counterborepocket structures have a keyhole shape with a first portion overlyingthe through-hole, with a first diameter, and a second portionoverlapping the first portion, having a second diameter greater than thefirst diameter.
 12. The fluidic assembly substrate of claim 11 whereinthe through-hole is offset from the first diameter center, away from thesecond portion.
 13. The fluidic assembly substrate of claim 9 whereinthe counterbore pocket structures have a keyhole shape with a firstportion overlying the through-hole, with a first diameter, and a secondportion overlapping the first portion, having a crescent moon-shape witha second diameter greater than the first diameter.
 14. The fluidicassembly substrate of claim 9 wherein the substrate is transparent. 15.A substrate assembly comprising: a substrate comprising a top surfaceand a bottom surface; a plurality of counterbore pocket structuresformed in the substrate top surface; a through-hole formed between eachcounterbore pocket structure and the substrate bottom surface; and, anobject at least sliding fit positioned inside each counterbore pocketstructure.
 16. The substrate assembly of claim 15 wherein the objectsare disks; and, wherein the counterbore pocket structures have a firstdiameter sliding fit to accommodate a disk diameter.
 17. The substrateassembly of claim 15 wherein the objects are disks; and, wherein thecounterbore pocket structures have a keyhole shape with a first portionoverlying the through-hole, with a first diameter transition fit toaccommodate a disk diameter, and a second portion overlapping the firstportion, having a second diameter greater than the first diameter. 18.The substrate assembly of claim 17 wherein the through-hole is offsetfrom the first diameter center, away from the second portion.
 19. Thesubstrate assembly of claim 15 wherein the objects are disks; and,wherein the counterbore, pocket structures have a keyhole shape with afirst portion overlying the through-hole, with a first diametertransition fit to accommodate a disk diameter, and a second portionoverlapping the first portion, having a crescent moon-shape with asecond diameter greater than the first diameter.
 20. The substrateassembly of claim 15 wherein the substrate is transparent; and, whereinthe objects are light emitting diodes (LEDs) in the form of disks.